reel them in real slow so they can adjust on their own. This is from the Ontario dnr hope it helps
Releasing Fish Caught From Deep Water
Releasing fish caught from deep water (more than 10 metres or 30 feet) can present special problems. Cold water species such as lake trout can rapidly equalize changes in water pressure. They can usually be released successfully regardless of the depth they came from, summer or winter. Warmwater species don't have this pressure-equalizing ability. Fish such as pike and walleye therefore should be brought to the surface slowly (to allow them to adjust to the change in pressure) and then be released immediately, if possible. Fish caught from deep water can be released by allowing them to slip out of your wetted hands head first into the water, while you are in a standing position. This not only heads the fish in the right direction, but also sends a blast of oxygen through its gills.
Utah dnr is not so optimistic tho.
When fishing deep water (deeper than 30 feet) most fish caught cannot be released with any assurance that they will survive. Bringing fish up quickly causes blood chemistry changes as well as an expansion of the air bladder to many times it's normal size, often causing it to protrude out of the fish's mouth. Keeping the fish in the water and quickly releasing it so it can get back down to deeper water helps some. Puncturing the swim bladder with a needle ("fizzing") does not improve survival. Some fish like lake trout can burp off the gases from the swim bladder when pulled up slowly. Most fish do not have this capability.
